Many commercial, industrial and government facilities require a significant number of lighting fixtures for adequate illumination, and therefore use a significant amount of power to operate the lighting fixtures. A number of facilities use lighting control systems to control when the lighting fixtures are energized and thereby reduce the amount of power that is consumed to light these facilities. Lighting control systems can include passive infrared (PIR) wall switch sensors that can be used to automatically power up incandescent or fluorescent lighting fixtures upon detection of occupant motion, and to power down the fixtures after a predetermined period of time has elapsed following the last instance of detected motion. This period of time shall hereinafter be referred to as the time out (TO) period.
In addition to a motion detector such as a PIR sensor and a control input to set the TO period, an occupancy sensor can be provided with an ambient light sensor and control input therefor. The ambient light sensor and control input can be used to select a minimum level of light above which a lighting fixture is prevented from being switched and powered on following detected motion. Thus, the lighting control system operates in a daylight inhibit mode when the ambient light level is sufficient to render the switching of the lamp unnecessary.
An existing occupancy sensor provides two indicators (e.g., two different colored light emitting diodes or LEDs) to indicate detected motion, and to indicate whether or not the ambient light level is sufficient to render the illumination of the fixture unnecessary following detected motion. The indicators are two LEDs and are disclosed in U.S. Pat. No. 5,699,243 which is commonly assigned to Hubbell Incorporated of Orange, Conn. and expressly incorporated herein by reference. As shown in FIG. 1, a red LED 24 is operated in a solid illumination mode when the lighting fixture associated with the occupancy sensor is powered down and the lighting control system is not in the daylight inhibit mode. The red LED 24 is toggled off when motion is detected. The green 26 LED is driven in a solid illumination mode when the lighting fixtures are powered down and then toggled when motion is detected to indicate that the lighting control system is in the daylight inhibit mode. In other words, the lighting fixture will not be powered on following motion detection because the ambient light level is sufficient. Thus, the red and green LEDs provide feedback to a user regarding the lighting control system's functional state, and aid remotely located customer service personnel when helping an occupant identify which mode the system is in and whether or not it is malfunctioning.
Exisiting room occupancy sensors are disadvantageous because TO period adjustment and operation cannot be controlled to maintain lighting fixtures in an active or inactive state regardless of detected motion and ambient light level. For example, setting the ambient light level for daylight inhibit mode can be difficult if lighting fixtures are switched on during the level setting process. The operation of the lighting fixtures during this process changes the detected amount of ambient light level to a higher foot-candle level than desired. A need exists for a system which temporarily bypasses operation of the lighting control system in response to detected motion and which provides an indication of this bypass mode of operation, among other functions.